Conventional wavelength division multiplexing (WDM) transmitter arrays may employ semiconductor lasers as optical transmitters. The performance of WDM systems depends on the signal integrity from the laser sources, which may fluctuate due to variations in the environment (e.g., temperature, etc.) and/or conditions of the laser (e.g., age, quality control in the manufacturing process). A general dichotomy exists between Coarse WDM (CWDM) networks and Dense WDM (DWDM) networks, in that CWDM networks may comprise a relatively wide channel spacing (e.g., about 20 nanometers (nm) or about 2500 Gigahertz (GHz), while dense WDM (DWDM) networks may comprise a relatively narrow channel spacing (e.g., about 0.8 nm or about 100 GHz). Accordingly, CWDM networks may comprise substantially fewer channels (e.g., up to about 18 channels) than DWDM networks (e.g., up to about 128 channels). Typical CWDM networks and DWDM networks may be described in International Telecommunications Union (ITU) Standardization Section (ITU-T) publication G.984.2 and ITU-T G984.1 (respectively), both of which are incorporated herein by reference as if reproduced in their entirety.
Due to their respective channel spacing, signal integrity may be more critical in DWDM networks than in CWDM networks. For instance, while a relatively small fluctuation/variation in signal integrity (e.g., wavelength drift) may be acceptable in CWDM networks, an equivalent variation may substantially reduce service quality in DWDM networks. Consequently, many CWDM systems may implement some strategy for correcting wavelength float. One strategy for correcting wavelength float is to provide wavelength locking via a feedback system that compares the actual laser output wavelength to the target laser output wavelength. Such feedback systems may employ a wavelength locker (λ-locker) to detect a difference between output and target wavelengths (e.g., a wavelength deviation), and an element manager to adjust the laser output accordingly. Specifically the λ-locker may detect the wavelength deviation by comparing a reference signal to a signal transmitted through an etalon to determine a signal differential, e.g., a difference in phase, amplitude, frequency, or combinations thereof, which may correspond to the output signal's deviation from the target wavelength. As such, the λ-locker may use the signal intensity differential to determine the wavelength deviation, which may be communicated to the element manager so that the laser's output can be adjusted accordingly. Wavelength locking techniques may be described in greater detail in U.S. patent application Ser. No. 12/579,196 filed on Oct. 14, 2009 by Hongbing Lei et al., and entitled “Wavelength Locker for Simultaneous Control of Multiple Dense Wavelength Division Multiplexing Transmitters”, which is incorporated by reference herein as if reproduced in its entirety.
Conventional distributed wavelength locking schemes may employ one dedicated λ-locker for each downstream channel (i.e., one λ-locker per transmitter), thereby using a separate λ-locker to provide wavelength locking to each respective laser source. Specifically, a dedicated wavelength locker may be located between each of the optical transmitters and the optical multiplexer and may be configured to detect wavelength float in each optical transmitter's output signal before the plurality of output signals are multiplexed into a WDM signal. However, λ-lockers may be relatively expensive such that networks employing more λ-lockers (e.g., dedicated λ-lockers, or one λ-locker per channel) may be substantially more expensive that those that employ fewer wavelength lockers (e.g., one λ-locker for multiple channels). For instance, conventional centralized wavelength locking schemes may employ a centralized λ-locker (e.g., a single λ-locker for all channels), and hence may be a cost effective alternative to conventional distributed networks. Specifically, the centralized λ-locker may be located downstream from the optical multiplexer, and may be configured to detect wavelength float in a plurality of channels in the WDM signal.